Molded articles made from cycloolefin polymers such as thermoset poly(dicyclopentadiene), the preparation of which is described in U.S. Pat. No. 4,400,340, are typically painted with a topcoat such as a white acrylic-urethane enamel. It has been found that in many instances poly(dicyclopentadiene) articles demonstrate poor ability to retain paint coatings. It is highly desirable for products made from this polymer to be painted, both to withstand degradation and for aesthetic reasons. In addition, a painted surface reduces any objectionable odor produced by unreacted dicyclopentadiene (DCPD) monomer remaining in the polymer. It has been known to treat polymers made from this monomer with a wash to reduce this odor. However, heretofore it has not been known that a surface treatment of sodium hypochlorite would increase the paint adhesion properties of dicyclopentadiene polymers.
In Japanese published patent application 62201940, dated Sept. 5, 1987, molded products were treated with a water solution of acidic, basic and/or amphoteric compounds to remove the residual odor of the dicyclopentadiene monomer in the polymer. Specifically, a solution of sulfuric acid was used.
Orlov, et al. in U.S. Pat. No. 3,869,303 discloses a method of surface modification of synthetic rubbers with an aqueous solution of a mineral acid, a mineral oxidant such as potassium permanganate and sodium perchlorate, and a salt of hydrochloric, hydrobromic or hydroiodic acid.
Jyo, et al. in U.S. Pat. No. 3,968,316 disclosed a surface treatment of synthetic resin containing ethylenic unsaturation by an alkyl hypohalite and a compound containing an active hydrogen and a functional group such as t-butyl hypochlorite in t-butyl alcohol.
In British Patent No. 1,396,090, dated May 29, 1975 a surface treatment of shaped, unsaturated rubber articles was disclosed which increased the articles bondability to other surfaces or a coating. The treatment was by contacting the rubber article with an alkyl hypohalite or a halogen-substituted alkyl hypohalite.
In Italian Pat. No. 720,390, a method of treating the surface of polyethylene or polypropylene was shown which increases the adhesion of the polymer to leather articles. The treatment was by a strong oxidizing agent selected from potassium dichromates or permanganates, potassium or calcium perborates, chlorites or hypochlorites or sodium peroxide.
Since it was found that in the production of molded poly(DCPD) articles that many such articles had poor paint adhesion properties, a solution was sought. One solution was the pretreatment of the parts with an adhesion promoting primer consisting of chlorinated polyolefin and ethylenevinylacetate copolymer. The pretreatment did promote excellent levels of paint adhesion, but it was only a temporary solution due to the significant added expense of the adhesion promoter and the additional manhours necessary for this pretreatment step. A study of the problem revealed that as polymer articles aged, the paint adhesion characteristics improved. However, it would be impractical to wait several weeks between the molding and painting steps. It was found that as molded articles aged the degree of surface oxidation increased and that there was a direct correlation between the degree of surface oxidation and paintability, with greatly improved adhesion of paints to the oxidized surfaces. Antioxidants had been added to the precursors of the polymer to maintain other properties, but it seemed that it would be necessary to promote oxidation in the surface of the article in order to improve paint adhesion. One approach to achieving oxidation of the surface of the article was to bake the item for a period of time. However, this did not increase the paint adhesion properties. This approach may not have been expected to improve paint adhesion properties since the articles demonstrating poor paint adhesion had passed through ovens at 160.degree. F. before application of the paint as well as a heated zone of up to 160.degree. F. after paint application. Heat alone did not change the surface of the polymer sufficiently to improve paint adhesion.
An aqueous solution of potassium permanganate was found to improve the adhesion of paints when applied to the molded articles. The potassium permanganate would be useful for certain applications, but due to the potential handling problems in the production facility, it was considered to be desirable to pursue alternative methods of improving the paint adhesion. A 30% solution of hydrogen peroxide was found not to improve the paint adhesive properties of the polymer. A method found to significantly improve paint adhesion was to expose an article to light in the ultraviolet range before applying the paint. Exposure to both high and low intensity ultraviolet light greatly improved the paint adhesion properties of the polymer. However, the introduction of ultraviolet lamps into the production line would require additional processing time and space. An inexpensive solution to the problem was needed which would not interfere with the production procedures. Such a solution has been found in this invention through the application of a solution of sodium hypochlorite to the article's surface before it is sent through the painting operation.